This piece is simply awesome, the dynamics breathtaking and the textures fit the character so well...
As for critique: If I was really nitpicky I would say that the character's left leg looks like it begins lover than the other leg and it's rotated in kinda painful position. And the right arm seems too thin to me.
But that all might be just me making out mistakes to write something.
Now this is impressive. There's a lot of energy and fury, not just in the pose of your figure, but in the color and thorny motif. It had a slightly hellish feeling to it.
I wish I could provide some useful commentary, but I don't know what I'd alter in this picture. It's amazing, it really is. Great work!
I completely agree with Vaxillus, the blue really draws the eye of the viewer, I wish I could give you a stronger critique, but I don't see anything wrong with the illustration, I think the shadows on the character pop her out from the background quite well.